1. Field of the Invention
This invention relates generally to the field of inductors and more particularly to hybrid circuit tunable inductors.
2. Description of the Related Art
In the manufacture of electronic equipment inductors are often used. Particularly, the microelectronics manufacturing industry frequently uses them, therefore the miniaturization of such components is of critical importance. In many cases during manufacturing, a circuit must be assembled first and thereafter tested. If upon testing the circuit is not within operational or desired limits, component replacement is required. Such replacement is both time consuming and expensive.
In recent years variable and tunable inductors have been used in the manufacturing process. Such an inductor may be formed within a hybrid circuit (one wherein some of the components are formed by conductors on an insulator or substrate) or a separate adjustable inductor element can be used. The need for miniaturization and performance has made the separate adjustable inductor ineffective. Due to its miniaturization, the inductor formed within a hybrid circuit is usually capable of being tuned using a laser or electron beam to remove or alter the inductor.
These variable inductors are manufactured into a circuit and then tuned to within operational limits. There have been a number of basic ways of achieving this goal. Often a spiral shaped inductor or a ladder or "U" shaped inductor with parallel shorts is used. Both of these have been useful in the current art, and both are commercially and industrially feasible.
The spiral inductor is space efficient; for a given tunable range the inductor takes very little space. The drawback to the spiral inductor is that the breaching of shorts across the spiral segment produces results that are not precisely predictable and of coarse granularity; thus it is not finely tunable. Such inductors, if designed for precision, with many tunable shorts, are very difficult to manufacture and add significantly to the cost. When the inductor is designed and manufactured with a smaller number of shorts, the inductor is useful and cost effective for applications where a broad range of values must be accommodated and component space is critical. It is not useful for applications where precision is critical.
The ladder or "U" shaped inductor is useful where fine tuning is required but space is not a premium consideration. Its inductance can be varied by breaching a short across its vertical legs. Here, however, the variance is substantially predictable and correlates highly to the number of, and spacing of the rungs. While such an inductor is useful for applications where precision is mandated, the space required per unit change of inductance is much greater than that of the spiral inductor.
Thus, using either of the aforementioned techniques has serious limitations; the former in terms of tuning precision, and the latter in terms of size and space requirements.